Wladimir Klitschko is the first name that came to mind. Taylor is a head case, but he still has a great jab. For some reason, Rafael Marquez is another name that came to mind. I guess anyone with good fundamentals and heavy hands is typically going to have a solid jab.
Rafael Marquez' is a ****ing piledriver. He had Silence Mabuza hurt with a jab. Vitali's is pretty powerful but otherwise it's shite.
david haye has a monster jab; sugar ray leonard had a very hard and fast jab. buster douglas comes to mind as having a very hard jab as well.
Ike Quartey's jab and left hand was something to behold it really was. Shame about the right hand though.